It is well known that steel surfaces will corrode in the presence of acid environments. While the rate at which corrosion will occur depends on a number of factors, such as the steel alloy itself, the strength and type of acid, the temperature of the environment, the length of contact, etc., some sort of corrosion invariably occurs. Alloy technology has provided materials to withstand the incidental contact of steel with acid, but the corrosion problem is particularly aggravated when there is no choice but to contact steel with acid, as in the case of chemical processing where acids are employed. In instances where the acid is not required to remain pure and where the contact is inevitable, attention has turned toward providing corrosion inhibitors in the acid medium itself to prevent corrosion of the steel surfaces that it must come into contact with, yet still deliver the acid to its ultimate destination. It would be advantageous if a new corrosion inhibitor were discovered that would be an improvement over the presently known systems. For example, a corrosion inhibitor providing a large corrosion inhibiting effect for a small proportion used would be advantageous. Additionally, there are presently no known effective high temperature HCl corrosion inhibitors for chrome steels such as Chrome 13 (CR 13) and 2205 duplex.
A specific environment in which an improved corrosion inhibitor would be appreciated is in the oil patch. It is well known that during the production life of an oil or gas well, the production zone within the well may be chemically treated or otherwise stimulated to enhance the economical production lifetime of the well. A common way of doing this is by acid fracturing or matrix acidizing, whereby a highly acidic solution, generally having a pH of less than about 1, but which may be as high as about 6.9 is injected into the well. Because of the acidic nature of the treatment fluid, the production or workover conduit which is utilized in the well in such applications encounters considerable acidic corrosion, in the forms of surface pitting, embrittlement, loss of metal component and the like.
In earlier years of producing subterranean wells, the vast majority of production and workover conduits which were utilized either temporarily or permanently in the well and through which a treatment or stimulation fluid was introduced into the well comprised carbon steels, such as J-55, P-105, N-80 and the like. Recently, due primarily to the drilling and completion of many subterranean wells through formations which contain high concentrations of corrosive fluid such as hydrogen sulfide, carbon dioxide, brine, and combinations of these constituents, the production and workover conduits for use in the wells have been made of high alloy steels. The high alloy steels, such as those employed herein in the description of the invention, include chrome steels such as 13 chrome and 2205 duplex steels and the like.
Stainless steels, first commercially developed in the 1920s, obtain their corrosion resistance by incorporation of a surface oxide film or adsorbed oxygen, of about 10 to 100 angstroms thickness. These stainless steels may be classified by their general structure and properties as: (1) martensitic; (2) ferritic; (3) austenitic (4) duplex; and (5) precipitation-hardening steels.
Martensitic alloy steels are magnetic and are hardenable by heat treating procedures. In subterranean well environments, they may be used for mild corrosion and high temperature service. Typical of such martensitic alloys is UNS S41000 (alloy 410) which contains from about 11.5% to about 13.5% chromium, about 0.15% carbon and no nickel.
Ferritic alloys are similar to martensitic alloys in that they, also, are magnetic. However, ferritic alloys are not hardenable by heat treatment and have corrosion resistance between alloys 410 and 304. They are also immune to chloride stress corrosion cracking and have a ductile to brittle transition temperature which somewhat limits their use in subterranean oil well environments. Exemplary of such ferritic alloys is UNS Sb 44735, which contains from about 28.0 to about 30.0% chrome, about 1% nickel between about 3.6% to about 4% molybdenum, and trace amounts of copper, nitrogen, titanium and niobium.
Austenitic stainless steels are non-magnetic and hardenable by cold work, and, like ferritic alloys, are not hardenable by heat treatment. Typical of such stainless steels in UNS S31603 (alloy 316L), which contains from about 16 to about 18% chrome, from about 10 to about 14% nickel, with traces of copper and molybdenum. Also typical of such austenitic stainless steels is UNS N08020 (alloy 20): UNS N08825 (alloy 825); and UNS N08904 (alloy 904L), which contains from about 19 to about 23% chrome, from about 23 to about 45% nickel, and from about 2 and about 5% molybdenum, with small percentages of copper along with other elements. Variants of these steels, such as S31254, N08026 and N08925, which contain up to about 6% molybdenum, are also classified as austenitic stainless steels and have high chloride resistance, and are particularly effective when used in and exposed to such environments.
Duplex steels combine ferrite and austenitic steels and have 2 to 3 times a yield strength of the austenitic stainless steels. A duplex stainless steel family is resistant to pitting and crevice corrosion and has significantly better CSCC resistance, than do the 300 series stainless steel products. Such steels have favorable toughness and ductility properties, with a coefficient of expansion nearer to that of carbon steel, thus reducing stress problems. Heat transfer in such stainless steels is about 25% greater than that of the austenitic steels.
Precipitation-hardened stainless steels attribute their high strength to the precipitation of a constituent from a super-saturated solid solution through a relatively simple heat treatment but do not encounter a loss in resistance to corrosion or ductility. These steels may be heat treated. Typical of such steels are UNS S17400 (17-4PH) and UNS S15700 (PH 15-7 Mo), which contains from about 14 to about 16% chromium, and from 2 to about 3% molybdenum, with from about 6.5% to about 7.8% nickel.
Other high alloy steels include those having high nickel content. Typical of such high nickel alloys are UNS N10276 (alloy C-276); UNS N06625 (alloy 625); and UNS N06110. These high nickel alloy materials are used to prepare tubular goods for subterranean wells, and other components for use within subterranean wells where such as use is expected to encounter extremely corrosive environments. The high nickel alloys have high tolerance to extremely hostile environments and typically contain about 60% nickel, from about 15 to about 20% chromium, and from about 9 to about 16% molybdenum.
U.S. Pat. No. 3,773,465 presents a typical teaching with respect to treatment of a low alloy, or N-80-type production conduits with intensified acid corrosion inhibitor compositions, and discloses the use of cuprous iodide in such treatment. Halohydroxyalkylthio-substituted and dihydroxyalkylthio-substituted polycarboxylic acids and alkali metal salts thereof are taught as effective corrosion inhibitors for various metal surfaces in U.S. Pat. No. 4,670,163. In one embodiment, mineral acid compositions such as aqueous hydrochloric acid metal cleaning solutions exhibit diminished corrosiveness when corrosion inhibiting additives of the invention are present in the compositions.
U.S. Pat. No. 4,498,997 relates to a method of acidizing a subterranean formation or well bore employing an acidic solution containing a corrosion inhibitor composition having an inhibiting effective amount of an acetylenic alcohol, a quaternary ammonium compound, an aromatic hydrocarbon and an antimony compound intensifier. Acetylenic compounds as inhibitors are also noted as effective by P. A. Burke, et al. in "Corrosion of Chromium Steels in Inhibited Acids," Corrosion/87, Paper No. 41, National Association of Corrosion Engineers, San Francisco, Calif., 1987, U.S. Pat. No. 4,552,672 describes an improved system over the one of the '997 patent, where the improved system also contains a stabilizer to substantially prevent precipitation of solubilized antimony-containing compounds from the aqueous solution. Related to the '997 and '672 patents is the discussion of propriety blends of acetylenic alcohols, dispersants, and heterocyclic quaternized amines, with or without formamide and inorganic salts which are examined for their corrosion inhibition properties in M. L. Walker, et al., "Inhibition of High Alloy Tubulars, II: Effect of Fluoride Ion and Acid Strength," Corrosion/88, Paper No. 189, National Association of Corrosion Engineers, St. Louis, Mo., 1988.
Further of interest is U.S. Pat. No. 4,683,954 which describes a method and composition for stimulating subterranean formations containing iron deposits, although it is not related to corrosion inhibition systems. The composition comprises an admixture of (i) at least one member selected from the group consisting of hydroxylamine hydrochloride, hydroxylamine hydrobromide, hydroxylamine sulfate, hydrazine monohydrochloride, hydrazine dihydrochloride, hydrazine sulfate, hydrazine monombromide, hydrazine dibromide, hydrazine monoiodide, hydrazine diiodide and hydroquinone together with (ii) at least one member selected from the group consisting of glucono-.delta.-lactone, citric acid, salts of citric acid, ethylenediaminetetraacetic acid, salts of ethylenediaminetetraacetic acid, nitrilotriacetic acid, salts of nitrilotriacetic acid, hydroxyethylehtylenediaminetriacetic acid and salts of hydroxyethylethylenediaminetriacetic acid, and (III) a catalytic amount of a solubilized salt of a compound capable of providing cupric, cuprous, nickel, zinc ions or mixtures thereof. The method involves contacting the formation in a manner and amount to sequester iron. It is noted that when the treating fluid is used in a formation that is substantially non-acidic that the compounds of group (ii), above, can be omitted.
It would be desirable if a new corrosion inhibitor or additive thereto could be discovered which would be an improvement over present techniques. The present invention relates to the use of an acid soluble mercury metal salt as an intensifier alone or together with a cuprous halide, in an acid corrosion inhibitor to retard the corrosion of steel, particularly chrome steel surfaces in acid environments.
U.S. Pat. No. 3,954,636 relates to a composition and method for the acid stimulation of subterranean formations, where the composition comprises a mixture of an acid which solubilizes at least a portion of the formation, an alcohol in which the acid and carbon dioxide are soluble, and a small proportion of water and carbon dioxide. The patent off-handedly mentions that a standard corrosion inhibitor and cupric chloride may be added to the mixture, but fails to indicate the purpose and details behind the cupric chloride addition.
Two methods for inhibiting stress cracking in stainless steel using mercury are set forth in U.S. Pat. Nos. 3,880,585 and 4,004,055. Both patents contain a discussion about how what is commonly called "stress corrosion cracking" is not believed by the inventors to involve much of a "corrosion" factor. The '585 patent teaches a method of inhibiting stress cracking in stainless steel articles exposed to a chloride-ion containing fluid environment in which the surface of the stainless steel article is contacted with a trace amount of an inorganic metal salt, such as mercuric nitrate, or with the metal corresponding to the cation of the salt, such as mercury. This is to enlarge the anodic areas on the surface and increase the uniformity of the electrical potential of the surface thereby eliminating concentrated non-uniform attack on the surface and attendant cracking. The method of the '055 patent also relates to inhibiting the stress cracking of stainless steel exposed to a chloride-ion fluid environment where the surface of the stainless steel is coated with at least a trace amount of metallic mercury. The invention therein also contemplates the mercury/stainless steel amalgam.